1. Field of the Invention
The present invention relates to a method for dry-spinning spandex at high speeds. More particularly, the invention concerns such a process wherein the spandex is dry spun and wound up at speeds as high as 900 meters per minute or higher from a solution of a polyurethaneurea derived from a polyether-based glycol that was capped with diisocyanate and then chain extended with a particular mixture of specific diamines. The spandex of the invention is especially suited for use in women's hosiery.
2. Description of the Prior Art
In dry-spinning conventional spandex, the combination of properties that can be obtained in the spandex is highly dependent on spinning speed. A particular combination of elongation and setting properties is needed in spandex intended for incorporation into women's hosiery. To assure that such hosiery will have a satisfactory appearance and appropriate elastic characteristics, the maximum spinning speed at which the spandex can be produced is limited. Higher speeds are needed for more efficient and economical production. However, at higher spinning speeds, typical conventional spandex compositions have significantly poorer break elongations and setting characteristics than are desired for spandex intended for use in hosiery.
In the conventional manufacture of women's hosiery, spandex yarns usually are knit into the hosiery along with nylon yarns. After knitting, the hosiery usually is subjected to a "boarding" treatment, in which the hosiery is placed on a form and treated with steam at a temperature of about 115.degree. C. The treatment remove wrinkles from the hosiery, sets the final shape of the hosiery, and provides the hosiery with a much more elegant initial appearance than such hosiery would have had were it not so treated.
Spandex yarns generally require higher setting temperatures than do nylon yarns. In boarding operations, excess temperatures or over-heating of the hosiery can cause formation of undesirable "board marks" or lines The undesirable marks correspond to the location of the edge of the form used in the boarding operation. Also, knit hosiery that contains spandex yarns generally does not retain the shape of the boarding form as well as does hosiery that contains no spandex, because of the strong elastic recovery properties of the spandex. These problems of spandex in hosiery are exacerbated with spandex of very low decitex. Nonetheless, over the years, the percentage of women's hosiery that contains spandex yarns has increased greatly because of the better recovery from stretch, the better fit retention and the better wear life possessed by such spandex-containing hosiery, compared to 100% nylon hosiery. Thus, there is a need for an improved spandex that can be produced at high speed and can be used satisfactorily in women's hosiery.
Though not concerned with the above-described problems of spandex in hosiery, Dreibelbis et al., U.S. Pat. No. 5,000,899, discloses a spandex that can be spun at speeds as high as 945 meters/minute. The spandex is set by a dry heat treatment at a temperature of about 190.degree. C. Such dry heat-setting conditions are suitable for heavyweight warp-knit fabrics. However, under the milder steam heat-setting temperatures typically used for boarding lightweight hosiery fabrics, the Dreibelbis et al products have very poor set. The Dreibelbis et al spandex is a polyurethaneurea formed from an isocyanate-capped tetrahydrofuran/3-methyltetrahydrofuran copolymer glycol that was chain extended with a diamine mixture, preferably of ethylenediamine ("EDA") and 2-methylpentamethylenediamine ("MPMD"). Generally, the amount of coextender in the diamine mixture is in the range of 20 to 50 mole percent. Among possible combinations of coextenders disclosed in passing by Dreibelbis et al (i.e., at column 3, lines 35-42) is a mixture of EDA and 1,2-diaminopropane ("PDA") coextender. A similar spandex yarn, formed from a capped glycol of a copolymer of tetrahydrofuran and 3-methyltetrahydrofuran that was chain-extended with an EDA/MPMD diamine mixture, is disclosed by Bretches et al, U.S. Pat. No. 4,973,647. However, the spandex of Bretches also suffers from shortcomings similar to those of the Dreibelbis spandex.
The use of mixtures of ethylenediamine ("EDA") and 1,2-diaminopropane ("PDA") and as chain extenders for polyether-based polyurethaneureas formed into spandex is also disclosed in Japanese Patent Application Publication 3-279,415, and Japanese Patent Application Publication 58-194915. The first of these Publications discloses such spandex made with EDA/PDA mixtures containing 10-30 mol % of PDA, (only 20% is exemplified) and then spun at a maximum speed of 300 meters/minute. The second Japanese Publication discloses such spandex formed from mixtures of diols that were reacted with a diisocyanate and then chain extended with an EDA/PDA mixture containing 1-40 mol % of PDA. The resultant polymer is then spun at a maximum speed of 210 meters/minute. Neither of these Japanese publications concerns the problems encountered in boarding spandex-containing hosiery.
An objective of this invention is to provide a process for high speed spinning of a polyether-based polyurethaneurea spandex that would be particularly suited for use in women's hosiery.